1. Field of the Invention
This invention relates to torque wrenches and, more particularly, to a signaling device for indicating that the wrench is applying a predetermined torque.
2. Description of the Prior Art
Torque wrenches are commonly used to apply a preselected amount of torque to a threaded fastener. These wrenches generally include a cylindrical torsion head which engages the threaded fastener at one end thereof. Extending radially from the torsion head is a resilient torque beam terminating in a handle. An indicating pointer is also attached to the torsion head at a point axially spaced from the torque beam. When the torque beam is in its relaxed position, the indicating pointer extends generally along the length of the torque beam. As a circumferential force is applied to the handle, the torque beam deflects, thereby applying a torque to the torsion head. However, the indicating pointer remains in substantially its original position. The deflection of the torque beam, and hence the magnitude of the applied torque, is measured on an indicating plate which is secured to the torque beam. As the torque beam deflects, the lateral offset between the pointer and beam which corresponds to the applied torque is read from a scale on the indicating plate.
In operation, a circumferential force is applied to the handle while the operator monitors the deflection of the torque beam by examining the position of the indicating pointer with respect to the numbers on the indicator plate. As the circumferential force increases, so does the beam deflection and applied torque until the lateral offset between the beam and indicating pointer reaches a predetermined value, as shown on the indicator plate.
Conventional torque wrenches are frequently used under conditions which make it difficult for the operator to read the scale on the indicator plate as he applies torque to the threaded fastener. For example, his vision may be obscured, there may be insufficient light, or his full attention may be focused on the threaded fastener. Under these circumstances, an excessive torque may be applied, possibly fracturing the threaded fastener.
For the aforementioned reasons, it is desirable to produce a torque wrench which generates an audio or visual signal when the wrench is applying a predetermined torque. Several devices have been devised which are somewhat adequate in performing this function. Examples of these devices are disclosed in U.S. Pat. No. 2,250,941, issued to Zimmerman; U.S. Pat. No. 3,076,362, issued to Able; and U.S. Pat. No. 3,142,177, issued to Hanscom, et al. A primary disadvantage of most of the prior art signaling devices is that the torque wrench must be specially designed to accommodate the signaling devices. This unduly increases the cost of these torque wrenches, particularly for those individuals already possessing a conventional torque wrench. Prior art torque signaling devices attachable to conventional torque wrenches do not adequately inform the user that the predetermined torque has been applied, and thus do not eliminate the risk of inadvertent fracture of the threaded fastener.